Symtoms : Start Jeep, and runs really rough at Idle and MIL flashes, and worse in gear for a minute or two, then seems to settle down, and I can drive it no problems. Only happens when I first start it...but notice when i go to park after a drive, it idles at around 500 rpm. MIL stays on (not flashing) throughout trip.

I cleared the codes with my Code reader, and ran the truck again (to see if it would run the same codes)...no problems at all...ran fine and the MIL stayed off. Took the truck on another trip about another hour later, again, ran fine and no MIL. Ran the truck again an hour after that, and it started fine, and ran ok, but the MIL came on about halfway (5 minnutes) into my trip. When i got home, I ran rhe code reader again, and got the same codes as above.

I have already changed and gapped the plugs (NGK platinum)...but an at a loss as to what could be setting off O2 sensor codes on 2 different banks??? I've also ran a tank of 93 octane gas...

I've looked through the forum and found that some have had luck with 'Seafoam'ing the engine (where in canada can I get that?) or by changing the Crank Sensor...

Any ideas before I throw a bunch of parts at this?

Greatly appreciate any help!
Thanks in advance..

PK

05WK

09-01-2012 12:56 AM

Re: 2005 Grand Cherokee 3.7 misfire

Id try the seafoam. Could just be carbon build up in your exhaust system or on the o2 sensors, in which case, seafoam should do the trick.

Id try your local autoparts store for the stuff or ordering offline somewhere. google is amazing with that stuff.

PKCherokee

09-06-2012 08:59 AM

Re: 2005 Grand Cherokee 3.7 misfire

Thanks 05WK...I did find a loacl store that carried Saefoam, and did it last weekend. I still get the random misfire, but do not get the 02 sensor error codes anymore, just the P0300 random misfire.
I just ordered a Crankshaft Position Sensor from my local NAPA and will try that as it's an inexpensive part to throw at it. Wish me luck!
Cheers!
PK

JMLoughrey

09-06-2012 09:08 AM

Re: 2005 Grand Cherokee 3.7 misfire

Get rid of the Platinum Spark plugs, the WK is a sensitive little beast and i would really only reccomend using the factory OEM (or champion equivalent).

2005JGC

09-06-2012 12:30 PM

Re: 2005 Grand Cherokee 3.7 misfire

I would look at the 02 sensor codes first possibly just o2 sensors but possibly an open wire somewhere or a poor connection, a problem is that if your o2 sensor is giving a false reading to an extreme then it will drive that banks adaptives WAY out of whack preventing proper combustion on that bank creating misfires.

PKCherokee

09-09-2012 12:33 PM

Re: 2005 Grand Cherokee 3.7 misfire

well for F sakes...this Crankshaft sensor is going to be the freaking death of me. Went to change it out today, and while trying to twist out the old one, I snapped it in half, right where the 'plate' joins the sensor that bolts to the engine. so now I have a stub in the block, with the copper leads hanging out of it. I've tried to get plies/vice grip in there, but it won't budge...first sprayed it with WD40, but now moved onto liquid Wrench...letting it sit now so hopefully I can get this thing removed tonight as I NEED my Jeep tomorrow...
yup...I'm screwed...

05WK

09-09-2012 04:53 PM

Re: 2005 Grand Cherokee 3.7 misfire

Dang, that sucks. best of luck!

baggee

09-12-2012 03:07 PM

Re: 2005 Grand Cherokee 3.7 misfire

When you decided to replace crankshaft (rpm) sensor you made mistake.You got a bad diagnose.RPM sensor can couse no start condition or interminent engine stall.It cant cause misfire codes.First you should try to replace spark plugs and look for broken or bad vacuum hoses,intake manifold leak or replace pcv valve.

2005JGC

09-16-2012 02:11 AM

Re: 2005 Grand Cherokee 3.7 misfire

I have given my .02... but what do I know its not like I do it for a living.

soontobesrt

09-16-2012 02:47 AM

Re: 2005 Grand Cherokee 3.7 misfire

I had same issue a few months back. First place to start if seafoam didn't work is swap the 02s. I had similar issue with misfires and then it went back to running rough. After puling the sensors they looked like they'd seen their fair share and wires were pretty dingy looking too. I did bank 1 as that was the codes I pulled and she fines for now. Im gonna ride bank 2 until one of those sensors goes and swap em both out. Bosch is way to go for those, good quality and handle the high temps better Ive heard, I just like the brand personally so I paid the few extra $ for it I guess haha.

If after swapping O2s you're stil getting the code for them it could be the wires touching on the exhaust or something cuasing it to short out/melt wires etc, very common. If they look clear and seem ok after a few days or riding around and you STILL get the 02 codes, then Id say you have a wiring issue before the connectors that may need some professional diagnostics to check over. Im pretty sure you wont see an issues though once you swap the sensors.

As for the crank sensor, thats unrelated to the issues you've described and they aren't a very common issue so not sure why you did that. If it was bad, it would throw a specific code almost certainly, same with the cam sensor. Playing the guess check system of can get expensive quick I know that, so be careful doing that. Anyway, IAC (idle air) valve deals with rough idles as does the TPS (throttle position) and are common issues of running rough at low idle, similar to shot 02s. The misfire is almost certainly caused by dead 02s though. Computer isn't seeing them and is sending way too much fuel causing this misfire which is what happend to me and likely was the last straw. These jeep just dont like to run w/o the 02 info not sure why as on many other vehicles, they just go back to closed loop and idle fine. Anyway. GL w/ the fix.

To get that crank sensor out Id run the motor a little and get it hot and then try to yank on it after hitting it w/ some pb blaster etc. Use longest wrench you can get in there (im sure its tight) and go to town, youll get it

Tb328

10-12-2013 09:05 AM

Re: 2005 Grand Cherokee 3.7 misfire

Thanks to all that posted on this topic - it's helped in troubleshooting. I had a p0300 code in an 06 3.7 wk with 80k mi that kept the check engine light on.

I've added ground straps to the compressor and alternator and linked them back to the frame at the battery terminal connection. Its passed the emissions inspection and the light hasn't been back for a few weeks. replacing the junk ground that's on the block (passenger side) connection may help also.